Ski area summer projects increase landslide risk

Mount Ashland is important to this region and the surrounding communities. It is a prominent asset and seen as a beacon — visible for many miles — occupying the highest elevation at the south end of the Bear Creek Valley. These factors mean we need to make certain all efforts are made to safeguard the difficult-to...

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By B.G. Hicks

MailTribune.com

By B.G. Hicks

Posted Jul. 26, 2013 at 12:01 AM
Updated Jul 26, 2013 at 2:10 AM

By B.G. Hicks

Posted Jul. 26, 2013 at 12:01 AM
Updated Jul 26, 2013 at 2:10 AM

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Mount Ashland is important to this region and the surrounding communities. It is a prominent asset and seen as a beacon — visible for many miles — occupying the highest elevation at the south end of the Bear Creek Valley. These factors mean we need to make certain all efforts are made to safeguard the difficult-to-control granitic soil terrain of this area. My comments were developed from long experience in the Ashland Watershed (for the U.S. Forest Service), and earlier in New Zealand studying debris slides, flows and avalanches.

The proposal by the Mt. Ashland Ski Area titled "Mt. Ashland Ski Area, Stormwater Pollution Control Plan, 2013, Summer Projects" along with supplements and a monitoring plan (available by Google search) describes plans to manage work on current long-term erosion and new problems resulting from: (1) parking area expansion producing material for reducing the slopes of two ski runs, (2) controlling drainage water, and (3) logging/vegetation removal along the ski run expansions.

The surface erosion that these plans address in the ski area is just the tip of the iceberg. Landsliding is not sufficiently addressed in the 2013 Summer Project report nor by current/ongoing Ashland Watershed management. The destructive storms of the recent past (1964, 1974, 1996-97 and earlier) caused many debris slides. These joined in major stream canyons to form torrential debris flows and sediment-laden flood waters that damaged the city water treatment plant, caused city flooding and water supply impairment and significant structural and private industry damage (lest we forget!).

This summer project involves three types of potential hazards from landsliding for which study and special construction are needed but not included in the plans:

1. Fill material use from the parking lot excavation to reduce the slope of ski runs: This granitic material is difficult to prevent from landsliding and erosion even when compacted or used as fill. Revegetation, a slow and difficult process, is not consistently successful in this ski area. (Expect problems later.)

2. Pond construction to collect sediment runoff: Avoiding failure in the granitic material used in pond construction requires detailed specific design and construction procedures for each site — not included in the present plan. Monitoring even during storms is inadequate and cannot guarantee pond stability. (Thus landslide failure of fills is likely.)

3. Ski run widening by logging can result in debris slides — probably a low hazard. Study and monitoring are required.

Landslides in the existing ski area and proposed expansion area were mapped by Dan Sitton, engineering geologist for the Rogue River National Forest in 1988-1989. Sitton presented the study at the 1989 International Geological Congress at Washington, D.C. In 1998 the study was included in a paper published by the Association of Engineering Geologists in "Environmental, Groundwater, and Engineering Geology: Applications from Oregon" titled "Landslide Mapping on the RRNF" and authored by Sitton and myself.

This mapping revealed a wide range of shallow to moderate depth landslide-type failures and debris eroded channels ("gutted channels"). The approximate area mapped was 1,800 acres extending downslope about 4,000 feet below the existing and proposed ski expansion areas. The mapped slides ranged from very narrow up to 200 feet in width. Mapping revealed about 73 slides of all types; an estimated one slide for approximately 24 acres or 25 slides per square mile and 3,300 feet of gutted channels commonly below slides. Therefore evidence shows — landsliding and their effects are common to the ski area (and watershed) and can, again, severely damage the community with debris avalanche enhanced massive flooding and property destruction.